1. Field of the Invention
The present invention relates to an emphasis-adding system and an emphasis-adding method for giving emphasis to a test signal serving as an original signal.
In this emphasis-adding system and the emphasis-adding method, emphasis is given in order to overcome waveform distortion of a test signal that is input via a transmission path such as a coaxial cable to a device-under-test such as a circuit-mounted substrate attached with a connector having a fast bus.
2. Description of the Related Art
For example, when a circuit-mounted substrate attached with a connector having a fast bus, which is low-cost but operating at a high rate, is adopted as a device-under-test (DUT), and a digital signal is input to the device-under-test using an electric signal or an optical signal via a coaxial cable, a waveform quality of a digital signal is deteriorated by the characteristics of the device-under-test. Accordingly, based on the deterioration of the waveform quality, bit error rate and jitter increase, and an amplitude of a waveform is changed. This may cause an adverse effect such as changing the shape of the eye pattern.
In this case, when this kind of deterioration of the waveform quality of the device-under-test is tested, a measurement system 100 as shown in FIG. 9 is generally used. In the measurement system 100 as shown in FIG. 9, a signal generation device 101 is connected to an input side of the device-under-test (DUT) W, and an error rate measurement device 102 is connected to an output side of the device-under-test W. In this measurement system 100, a test signal of a predetermined pattern is input from the signal generation device 101 to the device-under-test W, and an error rate measurement device 102 receives a signal that is output from the device-under-test W in accordance with the input of the test signal. Then, the error rate measurement device 102 compares the reception signal with the test signal that is input to the device-under-test W, measures the bit error rate, and measures the eye pattern, thus performing various kinds of tests of the device-under-test W.
However, when a non-pre-emphasized test signal is input, as it is, to the device-under-test W via the coaxial cable in the measurement system 100 as shown in FIG. 9, the signal is distorted as the frequency gets higher, and the signal is attenuated. This signal distortion deteriorates the bit error rate, and there is a problem in that the bit error rate cannot be correctly measured.
Accordingly, pre-emphasis given to the test signal serving as the original signal has been suggested as an effective solution for faithfully generating the test signal by compensating the attenuated portion of the signal in order to overcome the above distortion of the signal. For example, a technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2008-271552 is known as a system and a method for generating this pre-emphasized signal.
In the system and the method disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2008-271552, an input file including digital data representing a digital data pattern waveform is received, and the digital data are up-sampled with Fs/Fd rate. In this case, Fs denotes a sampling frequency, and Fd denotes a data rate. A step response is generated using the up-sampled digital data. The generated step response is differentiated, and a coefficient for pre-emphasis filter is generated. This coefficient and the digital data pattern waveform input signal are convoluted to generate a pre-emphasized digital data pattern. As a result, generation of various kinds of pre-emphasized signals is realized with the data generation system.
By the way, a pulse pattern generation system disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2005-094172 is known as a system for generating a desired pulse pattern that is input to the device-under-test. As shown in FIG. 10, in the pulse pattern generation system disclosed in the publication, numerical values are increased/decreased by directly inputting values to text boxes 110, and an amplitude or cross point is set by moving scroll bars 111 within a predetermined setting range, so that a test signal having a desired pulse pattern is generated.
In this case, when a test signal input to the device-under-test is pre-emphasized, it is necessary to set parameters relating to the pre-emphasis in advance. When the setting method disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2005-094172 is employed as the setting of the parameters relating to the pre-emphasis, it is necessary to set each parameter by increasing/decreasing numerical values directly input to the text boxes 110 or by moving the scroll bars 111 within the predetermined setting ranges as shown in FIG. 10. Therefore, there is a problem in that it is cumbersome for a user to set each parameter. In the setting method disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2005-094172, there is a problem in that the user cannot imagine the generated pre-emphasis waveform and does not know which portion of the pre-emphasis waveform is manipulated. As a result, the user cannot intuitively set each parameter.